Tom Cotton was livid that top Secret Service officials had leaked unflattering information about a GOP congressman who had become one of the embattled agency’s highest-profile critics.

So the freshman Republican senator from Arkansas quickly settled on his payback: He would indefinitely stall ambassadorial nominees to Sweden, Norway and the Bahamas — a former White House counsel, plus two Obama campaign bundlers — until the administration investigated the Secret Service’s misconduct.

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It's not just Cotton holding up nominations. Republican senators such as Ted Cruz, John McCain and Chuck Grassley are deploying the tactic at an unprecedented level in their ongoing war with the White House. Right now, eight ambassadorial nominees are waiting on the Senate floor to be confirmed, and more than 100 other nominations are languishing in committee.

Cotton’s move to block several low-profile appointments might seem unrelated to the Secret Service imbroglio. But jamming up nominations is one of the last weapons the Senate GOP can use to hit back at the administration with Democrats able to filibuster legislation and President Barack Obama wielding his veto pen.

“This is about a constitutional clash between the executive and the Legislature,” Cotton said in a recent interview in his Senate office. “In divided government, one critical check that the Senate has is the power of confirmation.”

While Democrats are incensed by the blockade, Republicans say that’s hypocritical, arguing that Democrats started the nomination wars during the presidency of George W. Bush. But this year’s GOP Senate is taking it to new heights, moving nominees at about half the pace of 2007, when Democrats controlled the Senate during Bush’s last two years in office.

As of Tuesday, the current GOP Senate has moved 107 of Obama’s picks, according to aCongressional Research Service report obtained by POLITICO.By comparison, the 2007 Democratic regime confirmed 192 of Bush’s civilian nominees. Furthermore, Democrats say this Senate is on pace to confirm the fewest civilian nominees since the end of Ronald Reagan’s presidency, the earliest records tracked on congressional databases.

It’s a historic battle with the president that's likely to continue as Obama marches toward the end of his presidency with minimal relations with Republicans on Capitol Hill.

"These are the kind of people that can call — if not Barack Obama, [then] Valerie Jarrett, Denis McDonough — and ask what’s wrong," Cotton said. “The West Wing needs to know the gravity with which Congress treats this matter."

Senate Majority Leader Mitch McConnell (R-Ky.) has been quick to back his fellow Republicans, using his procedural power to force votes on just one nominee who faced a procedural “hold” this Congress: Attorney General Loretta Lynch. By comparison, Minority Leader Harry Reid (D-Nev.) overrode GOP holds nearly 100 times last year when he led the Senate.

Among the most egregious examples of unnecessary holds, Democrats say, has been Cruz’s work to stymie confirmation of Gayle Smith, nominated as director of the U.S. Agency for International Development, the primary clearinghouse for civilian foreign aid. The vacancy is drawing more scrutiny as the United States faces pressure to act on the Syrian refugee crisis.

“It’s never been worse. And that reflects a decision by the Republicans to deny to this president even the most critical appointments,” said Senate Minority Whip Dick Durbin of Illinois. Smith has “been sitting on that calendar for months. Ted Cruz has a hold on her. Ask him: What’s your objection to her? ‘No, no, I object to the Iran nuclear agreement.’”

Faced with such resolute opposition from the GOP, there are signs that the White House isn’t eager to push more high-ranking nominees to the Senate.

The president is not likely to nominate John King to replace Arne Duncan as secretary of the Department of Education; instead, with just a year remaining after Duncan’s resignation, Obama can skate for the rest of his presidency with an interim secretary of education, according to GOP sources. The Bureau of Alcohol, Tobacco, Firearms and Explosives has lacked Senate-confirmed leadership for months, and Deputy Director Thomas Brandon is expected to run the agency for the rest of Obama’s presidency, rather than risk another nomination fight over gun control.

But for dozens of other nominees hoping to serve Obama for his last 15 months, there’s no way to work around the Republican Senate. Currently, there are about 60 nominees awaiting floor action, and more than twice that waiting for committee approval.

McCain, the Arizona Republican who chairs the Armed Services Committee, was initially steamed over Senate Democrats’ unilateral change to confirmation rules for most executive and judicial nominations in November 2013, holding up a host of nominees as retaliation. Now, McCain says the same nominees will continue to linger in his committee — but this time, it’s over Obama’s continued threats to veto the National Defense Authorization Act.

“Until we fix the problem, why should they [be confirmed]?” McCain said. “They’re not agreeing to what’s necessary to protect and serve the men and women who are serving in the military. So why the hell should we support their civilians to support or work for a failed institution, a failed policy, a failed branch of government?”

Still, there may be ways around McCain’s bottleneck, particularly if the nominee in question has friends in high places.

Stephen Hedger was unanimously confirmed as assistant secretary of defense for legislative affairs last week after languishing for months and Peter Levine was confirmed in May as the deputy chief management director at the Pentagon. Both are former Hill aides: Hedger served as Sen. Claire McCaskill’s (D-Mo.) legislative director, and Levine was staff director for former committee Chairman Carl Levin (D-Mich.).

For all the complaints from Democrats, Republicans point to several similar uses of the Senate’s confirmation power when Democrats were in the minority or when Bush was president. Democrats used pro forma sessions to block Bush from making recess appointments — roadblocks that Obama also facedin his first years at the White House — and threatened to halt all executive branch nominees after a dispute with the Bush White House on the advise-and-consent process.

"They might want to look in the mirror before complaining about holds," said one senior Republican.

Increasingly, Republicans are coalescing around a new frontier in the nominations conflict: A State Department under siege over Hillary Clinton’s use of a private email server when she was secretary of state. Senate Foreign Relations Chairman Bob Corker (R-Tenn.) and his ranking member, Ben Cardin (D-Md.), agreed in interviews that their committee has processed nominees at an admirable rate. But when things come to the floor, that’s when it gets ugly.

Of the nominees idling on the Senate floor, about a third were cleared by the Foreign Relations Committee, which oversees the State Department. Aside from Cruz and Cotton, Senate Judiciary Committee Chairman Chuck Grassley is blocking State nominees over what the Iowa Republican says is insufficient cooperation with his inquiries over Clinton’s private email use and State’s Special Government Employee program that has drawn attention to top Clinton aide Huma Abedin.

“Most of our guys … don’t abuse it,” said South Dakota Sen. John Thune, the No. 3 Senate Republican. “They’re looking for legitimate opportunities to try and get the administration to pay attention and engage with them on something that’s important.”

Last week, the Senate approved a half-dozen ambassadors, despite Cruz’s declaration in July that he would block all State Department nominees over his displeasure with the Iran deal. A Cruz spokeswoman says the senator did not have a hold on any nonpartisan career Foreign Service officers, which was never noted in Cruz’s initial statement.

Though some senior Senate Republicans have privately grumbled that the State Department is getting hit with a disproportionate amount of the GOP nominations rage, there is optimism in both parties after last week’s ambassadorial breakthrough.

“We move ‘em out as quickly as is prudent. I think that’s our job, especially those that are career,” Corker said. On the floor, “I feel like maybe we’re beginning to loosen up just a bit. I do.”

But there’s no such hope for judicial appointments. Despite several confirmations in the past months, McConnell is still on pace for installing the fewest new judges since 1969 and is flirting with the most recent low of nine judicial confirmations reached in 1953. The Senate has approved only seven judges thus far as Republicans eye taking the White House in 2016 and installing their own conservative judges. Confirmation of an eighth judge is scheduled for next week.

GOP senators argue that lame-duck Senate Democrats pushed through a host of judges last year that Republicans would have otherwise taken up this year. But Democrats, pointing to 30 judicial emergencies in the short-staffed federal courts, are Impatient over the standstill.

“They’re up to about what, 20 percent of what we did for President Bush at this time?” groused Vermont Sen. Patrick Leahy, the top Democrat on the Senate Judiciary Committee. “No. I’m a 100 percent man.”